1. Field of the Invention
This invention relates to a salt of an anion of an active hydrogen compound in a form derived by elimination of protons from the active hydrogen compound, said salt being novel and extremely important for organic reactions. More specifically, the present invention is concerned with a novel salt of a phosphazenium cation and an anion of an active hydrogen compound or a novel phosphazenium hydroxide as an example of the salt and with its preparation process, and also with use of the salt or the hydroxide as an effective catalyst for the polymerization of an alkylene oxide compound.
A poly(alkylene oxide) is an important polymer useful as a raw material for the production of polyurethane foams and elastomers available through its reaction with organopolyisocyanate compounds and also as a surfactant.
2. Description of the Related Art
It has been well known for many years to convert an active hydrogen compound into an anion by taking a proton out of the active hydrogen compound and then to obtain its salt with a counter cation. Depending on the strength of acidity of the active hydrogen compound, various processes are used. For example, carboxylic acids, nitroalkanes, alcohols or phenols can be rather easily formed into salts through reactions with alkali metal hydroxides or in some instances, alkali metal carbonates or the like. For the formation of salts of ketones, alkylnitriles, cyclopentadienes, amines, amides or imides, it is a common practice to use alkali metals or compounds thereof such as alkali metals, alkali metal hydrides, alkali metal amides or alkyl alkali metals. The salts obtainable by these processes are however salts of anions derived from active hydrogen compounds and alkali metal cations. To make effective the reactivity of an anion of an active hydrogen compound, it is necessary to dissolve its salt in a solvent. However, solvents which can sufficiently dissolve a salt containing such an alkali metal cation are extremely limited. In some instances, the reactivity of an anion may be substantially affected by the size of its counter cation. If this cation is limited to an alkali metal cation, a limitation is imposed on the size of a cation.
Further, the hydroxides of alkali metals or alkaline earth metals are also extremely important compounds in the field of organic reactions for their basicity. To improve the effects of these hydroxides upon using them in organic reactions, it is important to dissolve them in an organic solvent. These hydroxide are soluble in water but are only sparingly soluble in general organic solvents. They hence have an unsuitable side effect for organic reactions which are apt to be easily impaired by water.
Industrial practice of an organic reaction by using a salt of an anion derived from an active hydrogen compound and an alkali metal cation or the hydroxide of an alkali metal or alkaline earth metal involves such problems as mentioned above.
Upon production of a poly(alkylene oxide) by polymerization of an alkylene oxide compound, it is most usual to use, as an initiator system, a combination of an active hydrogen compound such as a polyhydric alcohol and a basic alkali metal compound such as potassium hydroxide. Such initiator systems are also used in industry. Nonetheless, there is a desire for the development of an initiator system which is more efficient from the standpoint of polymerization activity and physical properties of a resulting polymer. Concerning initiator systems other than the combinations mentioned above, U.S. Pat. No. 3,829,505 discloses obtaining a polymer from propylene oxide by using an active hydrogen compound and, for example, a compound represented by Zn.sub.3 [Fe(CN).sub.6 ].sub.2.H.sub.2 O. dioxane. Japanese Patent Laid-Open No. 276821/1990 discloses obtaining a poly(alkylene oxide) by using zinc hexacyanocobaltate. Further, Japanese Patent Laid-Open No. 232433/1987 discloses obtaining a polymer by polymerizing ethylene oxide while using a reaction product which has been obtained by adding a solution of diethyl zinc in hexane to a dispersion formed by adding 1,4-butanediol and a nonionic surfactant to a slurry of fumed silica in hexane. These initiator systems all contain special metal components and, if these metal components remain in the resulting poly(alkylene oxide), they adversely affect reactions upon production of polyurethanes or physical properties of the polyurethanes so produced. A special process or complex steps are therefore needed for the full elimination of such metal components upon production of poly(alkylene oxide).
Concerning metal-free initiator systems, on the other hand, Japanese Patent Laid-Open No. 159595/1975 discloses preparation of a polymer from ethylene oxide by a combination of an alkane polyol, an active hydrogen compound, and an ether adduct of boron trifluoride. With respect to this initiator system, it is however also known that certain specific impurities in the polymer give deleterious effects on some physical properties of urethane. Cumbersome steps are thus required for their full elimination. Further, according to Japanese Patent Laid-Open No. 12026/1982, a polymer of an alkylene oxide is obtained using an alcohol and aminophenol. According to Japanese Patent Laid-Open No. 38323/1981, propylene oxide is polymerized using sorbitol and tetramethylammonium hydroxide. These initiator systems are however accompanied by problems such that their polymerization activities are not sufficient and moreover, an amine-like odor remains in the resulting polymers.